The goals of this project are to develop an electrical prosthesis for people who have impaired vestibular function, and to use the prosthesis to investigate the vestibular system in a way that is not feasible via mechanical means. This investigation will study the vestibular system in guinea pigs and squirrel monkeys by stimulating the vestibular nerve with modulated electrical pulses that contain signals at a variety of frequencies, and characterizing the sensitivity and phase of their angular vestibuloocular reflex at the same frequencies where the input has components. Another topic to be studied is adaptation of eye movements to electrical stimulation of the vestibular nerve. Initial stimulation is expected to cause inappropriate eye movements that are not compensatory for the animal's head movements. When electrical stimulation is applied chronically, these eye movements will be recorded and studied using the tools of spectral analysis, in order to closely monitor whether the eye movements adapt to the stimulation and discontinue (or reduce) noncompensatory components.